The present invention relates to an apparatus for state of charge compensation in a battery system having a series connection of a first battery sub-module and a second battery sub-module and having a first voltage conversion module, wherein an electrical component can be connected to the first voltage conversion module and can be supplied with the electrical energy from the connected second battery sub-module.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
To supply power to electrical components, electrical energy/power storage devices are generally provided. Such energy/power storage devices can be, for example, battery cells which provide a battery cell voltage. In order to provide a desired voltage level, the battery cells are normally interconnected to form battery stacks. In low-voltage applications, voltages of less than 60 V are usually provided, in high-voltage applications, voltages of more than 60 V, in particular of more than 100 V, are usually provided. Energy storage devices in high-voltage applications can be designed, for example, to supply power to electrical machines, e.g. electric motors in motor vehicles. In addition, capacitors, for example, can be used as electrical energy stores.
Particularly for high-voltage applications, the voltage of single battery stacks is generally insufficient. To achieve a higher voltage, in particular a voltage in the high-voltage range, it can be provided that a plurality of battery stacks is used to supply an electrical component, e.g. an electric motor. For this purpose a plurality of battery stacks are usually connected in series to form a battery system to which an electrical component to be supplied is connected. The sum of the voltages of the individual battery stacks is therefore available to the electrical component.
Because of possible different battery cell chemicals, aging effects, manufacturing tolerances and loading profiles, the battery stacks may exhibit differing charge states and different impedances. As a result, the series-connected battery stacks are discharged and charged differently during operation, in which case they may assume critical charge states. The different charge states are generally compensated using so-called state of charge compensation or balancing methods. Without appropriate balancing, service-life-extending and full utilization of the entire installed battery energy is impossible, or it would be necessary to accept an operating strategy that would limit a possible operating range of the battery system.
In the prior art, so-called dissipative balancing methods are currently mainly used. Here the battery stack or battery cell having the highest state of charge is discharged by converting the charging energy of said battery stack or battery cell into heat by way of a parallel-connected resistor. The excess energy of the more heavily charged battery stack or battery cell is therefore reduced via losses in ohmic balancing resistors. This balancing process is generally monitored by a battery management system.
These dissipative methods are generally energy-inefficient and involve high costs due to the complex monitoring by the battery management system.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved apparatus and a method for state of charge compensation which is energy-efficient and inexpensive and with which the service life of the battery system can be extended.